The Institute of Electrical and Electronics Engineers (IEEE) has produced a series of standards referred to as 802.X, which encompasses LANs (Local Area Networks), MANs (Metropolitan Area Networks) and PANs (Personal Area Networks) such as Bluetooth. The IEEE 802 dictates standardizing processes and procedures that take place in the bottom two layers of the OSI (Open System Interconnection) reference model—the media access control (MAC) sublayer of the link layer and the physical layer.
In the wireless local area network (WLAN) topology, each wireless network requires a radio transceiver and antenna. Components on the wireless network are either stations (STAs) or access points (APs). Typically, a station STA is mobile or portable, and the access point AP may be a permanent structure analogous to a base station tower used in cellular phone networks or to a hub used in a wired network. A basic service set (BSS) is formed when two or more stations have recognized each other and established a network. An extended service set (ESS) is formed when BSSs (each one comprising an AP) are connected together.
FIG. 1 illustrates the basic service set BSS 1 operating in the infrastructure mode, wherein a wireless network is formed between one or more stations (STA) 2 communicating with an access point (AP) 4 such as a communications tower. The access point acts as an Ethernet bridge and forwards the communications onto the network (e.g., either wired or wireless network). Several such BSS networks communicating together over the infrastructure between APs further form an Extended Service Set (ESS), or a Distribution System (DS).
Stations 2 are typically mobile or portable devices powered by batteries. Accordingly, power consumption of the stations is important to manage in order to extend operational life of stations 2 without requiring new batteries. The problem is to deliver multicast and broadcast packets in such a way as to minimize current drain in stations 2, while maintaining high spectral efficiency.
In the 802.11 standard today, an inefficient current-drain-saving means of delivering multicast and broadcast packets to stations exists. This method in the 802.11 standard is as follows. A beacon is delivered at regular periodic and predictable intervals. The stations that are not active in a call enter a low power mode, e.g. sleep, between beacons. The stations know when the next beacon will arrive because the arrival time of the next beacon is signaled in the current beacon. The stations awake at every beacon interval to read the DTIM signal present in every beacon. The DTIM will signal whether broadcast and multicast packets shall be delivered immediately after the beacon. If broadcast and multicast packets are to be delivered in this beacon interval, all stations shall stay awake to hear the delivery of broadcast and multicast packets. In each broadcast/multicast packet transmitted a more data control bit exists; if that bit is set in the broadcast/multicast packet, the stations stay awake to continue receiving broadcast/multicast packets; if not, all the stations will resume the low power mode, e.g. sleeping. If broadcast and multicast packets are not to be delivered in this beacon interval, all stations will resume the low power mode, e.g. sleeping.
There are some problems in this design. The delivery of the multicast/broadcast packets after the DTIM can be interrupted by inbound unicast transmissions. This will delay the delivery of the multicast/broadcast packets, keeping the stations awake longer than necessary. Because the stations don't know if all of the broadcast/multicast packets have been delivered until the more data bit is clear, the stations must stay awake for delivery of all of the multicast/broadcast packets. It is not mandatory that the multicast and broadcast packets be transmitted OTA in order of priority or even in order of arrival at the AP. As a result, the station must stay awake until all of the multicast/broadcast packets are delivered to ensure reception of all pertinent packets. Yet another problem is over the air packet error. In a typical 802.X system, over the air packet error is approximately 10%, and the system ensures delivery using an ACK based protocol. In such a system, the 802.X standard does not provide for reliable delivery of multicast frames and thus delivery of multicast packets is not ensured. Not having reliable delivery of multicast packets requires the station to stay awake to ensure reception of pertinent packets. Accordingly, there is a need for delivery in wireless communication networks.